A method for treatment of nitrified wastewater, the method including supplying wastewater to be treated to a tank having a layer of biomass supporting media near or at the top thereof, retaining biomass on and below the biomass supporting media for a sufficient time such that the biomass hydrolyses and supplies organic carbon to the wastewater in the tank; denitrifying and simultaneously clarifying the wastewater by providing an upward flow of the wastewater in the tank through the layer of biomass supporting media and discharging excess sludge from the bottom of the tank at a rate which is selected to maintain nitrate and ammonia concentrations below selected thresholds.